Summary

The root uptake of 134 Cs by forage plants was studied as a function of growth stage and N fertilization with biotite supplementation.The study was conducted by means of pot experiments with peat soil. In the growth stage studies,ryegrass,white clover and yellow-flowered lucerne were cut once 30,60 or 90 days after sowing or three times at intervals of 30 days.In the one-cut system, at 90 d,the activity concentration of 134 Cs in ryegrass and clover was higher and that in lucerne lower than in the three-cut system.In both treatments,the activity concentration in ryegrass decreased and that in legumes,generally,tended to increase with time.In the N fertilization studies,ryegrass was grown at different levels of ammonium nitrate (100,200 and 400 mg N l -1 )and biotite (0,10,20 and 40 g l -1 ) application.The addition of N to soil increased and that of biotite decreased the 134 Cs activity con- centration in ryegrass. The differences in forage 134 Cs between the two harvesting systems were small.Although ammonium nitrate increased the 134 Cs uptake by ryegrass,in the event of fallout, moderate rates of ammonium fertilizer could be used provided that biotite or K are applied at adequate levels.